In recent years, in accordance with the improvement of high functionality and multi-functionality of semiconductor devices, and of an operation speed thereof, the amount of heat generated by such semiconductor devices tends to increase. Hence, in the case of a multilayer wiring board that includes an insulation layer containing, for example, normal glass woven cloth or glass non-woven cloth, it is difficult to efficiently treat heat generated by a high-output power amplifier. In addition, according to this multilayer wiring board, an electromagnetic shielding effect, and an electromagnetic interference shielding effect are not expectable, and thus it is difficult to suppress an electromagnetic interference by shielding electromagnetic waves.
Measures to efficiently dissipate heat generated by a power amplifier are taken in a wiring board on which the power amplifier is mounted. According to conventional wiring boards, heat from the power amplifier is transferred to a heat sink provided on the wiring board via through-holes and conductor patterns. The heat sink dissipates the transferred heat to the exterior.
However, each through-hole does not have a sufficient heat transfer performance, and the dimension of the heat sink has a restriction. Hence, according to conventional technologies, it is difficult to mount a power amplifier that has a relatively large amount of heat generation per a unit area on the wiring board.
In addition, in recent years, researches and developments are enhanced to improve a transmission output by applying a gallium nitride (GaN) transistor for the power amplifier so as not to increase the dimension of a microwave transceiver. Since the GaN transistor has a large output, a total amount of heat generation and an amount of heat generation per a unit area are relatively large. Conversely, when cooling is insufficient, the operation becomes unstable, and the product lifetime becomes short. Hence, it is necessary to improve the heat dissipation effect in the wiring board in order to enable such a power amplifier to be mounted thereon.
In addition, conventional microwave transceivers are constructed by a combination of a metal plate, a casing which will be a heat spreader, and a monolayer board or a multilayer board. Conventional microwave transceivers have disadvantages in at least any one of a high-frequency performance (discontinuity of grounding), a reliability (a deterioration of joined portions due to a difference of thermal expansion rate of components), an electromagnetic compatibility, and a price.